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LieAlgebras[GradeSemiSimpleLieAlgebra] - find the grading of a semi-simple Lie algebra defined by a set of simple roots or restricted simple roots
Calling Sequences
GradeSemiSimpleLieAlgebra(1)
GradeSemiSimpleLieAlgebra(2, method = "non-compact")
Parameters
Sigma - a list or set of column vectors, defining a subset of the simple roots or a subset of the restricted simple roots
T1 - a table, with indices that include "RootSpaceDecomposition", "CartanSubalgebra", "SimpleRoots", "PositiveRoots"
T2 - a table, with indices that include "RestrictedRoot SpaceDecomposition", "CartanSubalgebraDecomposition", "RestrictedSimpleRoots", "RestrictedPositiveRoots"
Description
Let g be a Lie algebra. A grading of g is a (vector space) direct sum decomposition g =where Gradings of semi-simple Lie algebras can easily be constructed from the root space decomposition. Let h be a Cartan subalgebra and the associated root space decomposition. Let be a choice of positive roots and let be a set of simple roots. Every root α is a sum of simple roots, say and one defines the height of the root as ht.
Now let be a collection of simple roots and define the Σ height of as ht where the sum is taken over those such that . Then the subspaces
and
define a (symmetric) grading g =
For real Lie algebras, real gradings can be similarly constructed using the restricted root space decomposition.
The command Query/"Gradation" will test if a given decomposition of a Lie algebra is graded.
Examples
Example 1.
We calculate the various gradations for We use the command SimpleLieAlgebraData to initialize the Lie algebra.
We use the command SimpleLieAlgebraProperties to create a table containing the structure properties of .
Here are the possible subsets of the set of simple roots.
Here are the gradings defined by each subset of the simple roots.
The Query command can be used to check that each of these define a grading of .
Example 2.
We calculate the various gradings for We use the command SimpleLieAlgebraData to initialize the Lie algebra.
We use the command SimpleLieAlgebraProperties to calculate the restricted root space decomposition, restricted simple roots, etc.
The subsets of the restricted simple roots are:
Here are the possible gradings for
See Also
DifferentialGeometry, CartanSubalgebra, KillingForm, LieAlgebras, PositiveRoots, Query, SimpleRoots, RootSpaceDecomposition, RestrictedRootSpaceDecomposition, SimpleLieAlgebraData, SimpleLieAlgebraProperties
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